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Characterization and properties of new dielectric ceramics Ba_5LnZnNb_9O_(30)(Ln=La, Nd and Sm)

中国有色金属学会会刊：英文版 2006年第B02期16卷 534-537页

作者：朱文凤胡长征吴伯麟方亮 Key Laboratory of Nonferrous Materials and New Processing TechnologyMinistry of Education Guilin University of TechnologyGuilin 541004China Key Laboratory of Nonferrous Materials and New Processing TechnologyMinistry of Education Guilin University of Technology Guilin 541004China State Key Laboratory of Advanced Technology for Materials Synthesis and Processing Wuhan University of Technology Wuhan 430070 China

Three novel dielectric ceramics Ba5LnZnNb9O30 (Ln= La, Nd and Sm) were synthesized and characterized in the BaO-Ln2O3-ZnO-Nb2O5 quaternary system, which formed the filled tungsten-bronze structures. The present ceramics exhibit high dielectric constant (εr) up to 310, low dielectric loss in the level of 10 3 at 1 MHz. Meanwhile, the temperature coefficients of the dielectric constant (τε) of Ba5LnZnNb9O3o varies from -1 390×10-6 to -1 220×10-6/℃as the radius of Ln3+ increases. The present ceramics are promising candidates for high dielectric constant and low loss dielectric ceramics.

关键词：介电陶瓷 Ba5LnZnNb9O30 Ba5NdZnNb9O30 Ba5SmZnNb9O30 合成介电性质表征

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Research on shaping technology of nanocomposite WC-6Co powder and properties of sintered compacts

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International Journal of Nanoscience 2006年第2-3期5卷 233-238页

作者： Shi, Xiaoliang Shao, Gangqin Duan, Xinglong Yuan, Runzhang State Key Laboratory of Advanced Technology for Materials Synthesis and Processing Wuhan University of Technology 122 Luoshi Road Wuhan 430070 China

The influences of powder extrusfen molding (PEM), die pressing and cold isostatic pressing (CIP) on the green compacts and the sintered compacts of nanocrystalline WC-6Co composite powder produced by spray pyrogenation- continuous reduction and carburization technology were researched. The results showed that the pore volume distribution, density and scanning electron microscopy (SEM) morphologies of fractured surface of powder extrusion molding or die pressing followed by the cold isostatic pressing consolidation green compacts were better than that of powder extrusion molding or die pressing. The green compacts were sintered by using vacuum sintering plus hot isostatic pressing (HIP), the sintered specimens were characterized by testing density, Rockwell A hardness, saturated magnetization, coercivity force, transverse rupture strength (TRS) and atomic force microscope (AFM) images, the results showed that sintered specimen of the green body that prepared by powder extrusion molding or die pressing followed by cold isostatic pressing had excellent properties of high strength and high hardness, transverse rupture strength of sintered specimen was more than 3100 MPa, Rockwell A hardness of sintered body was more than 93. Ultrafine WC-6Co cemented carbide rods with excellent mechanical properties and fine microstructure were obtained. © World Scientific Publishing Company.

关键词： Nanotechnology

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Fabrication and properties of Ni-YSZ and Ni-Co-YSZ cermets

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International Journal of Nanoscience 2006年第2-3期5卷 225-231页

作者： Shao, Gang-Qin Li, Yong Duan, Xing-Long Cai, Hu Li, Jia Shi, Xiao-Liang Guo, Jing-Kun State Key Laboratory of Advanced Technology for Materials Synthesis and Processing Wuhan University of Technology 122 Luoshi Road Wuhan 430070 China

Ni-YSZ and Ni-Co-YSZ cermets were fabricated by hot-press-sintering from nanocomposite powders. The structure, morphology, relative density, hardness, specific heat capacity and thermal conductivity were measured. Results show that the crystalline grains are much homogeneous. Their size distribution is quite narrow and between 0.2-0.4 μm (200-400 nm). The Ni-Co-YSZ cermet reaches a maximum relative density (96.2%) at 1350°C and a maximum Rockwell hardness (70.5) at 1400°C. The specific heat capacity of Ni-YSZ cermet is larger than that of Ni-Co-YSZ cermet. The thermal conductivity of Ni-YSZ cermet is smaller than that of Ni-Co-YSZ cermet. © World Scientific Publishing Company.

关键词： Cermets

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Fabrication of monolithic bulk Ti_3AlC_2 and impurity measurement by K-value method

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中国有色金属学会会刊：英文版 2006年第B02期16卷 490-493页

作者：徐学文富成科李养贤朱教群梅炳初 School of Materials Science and Engineering Hebei University of Technology Tianjin 300130 China Hebei Communications Vocational & Technical CollegeShijiazhuang 050091 China School of Materials Science and Engineering Hebei University of Technology Tianjin 300130China State Key Laboratory of Advanced Technology for Materials Synthesis and Processing Wuhan University of Technology Wuhan 430070 China State Key Laboratory of Advanced Technology for Materials Synthesis and Processing Wuhan University of Technology Wuhan 430070 China

Polycrystalline bulk Ti3AlC2 material with high purity and density was fabricated by hot pressing from the powder mixture with the starting stoichiometric mole ratios of 2.0TiC/ 1.0Ti/ 1.1A1/ 0.1Si at 1 300-1 500℃. X-ray diffraction patterns and scanning electron microscopy photographs of the fully dense samples indicate that the proper addition of silicon is favorable to the formation of Ti3AlC2, consequently results in high purity of the prepared samples. The Ti3AlC2 hot pressed at 1 300℃and 1 400℃is in plane-shape with sizes of 6-8μm and 15-20μm in the elongated dimension, respectively. The purities of samples are measured by the K-value method, and the contents of TiC are given by a linear equation.

关键词：多晶单片Ti3AlC2陶瓷制造杂质纯度测量 Κ值法

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synthesis and X-ray Powder Diffraction Characterization of A New Niobate Crystal NaBa_2Li_(0.6)Nb_(4.8)Zn_(0.2)O_(15)

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Journal of Wuhan University of technology(materials Science) 2006年第1期21卷 1-3页

作者：欧阳世翕 State Key Laboratory of Advanced Technology for Materials Synthesis and Processing Wuhan University of Technology Wuhan 430070ChinaChina Building Materials Academy Beijing 100024China

A new niobate compound was synthesized for the first time in Na2 O-BaO-Li2 O-ZnO-Nb2 O5 system by solid state reaction. The acw compound was studied by X-ray diffraction, electron probe, X-ray microanalysis, chemical analysis and SEM. The result of X-ray powder diffraction shows that NaBa2 Li0.6 Nb4.8 Zn0.2 O15 belongs to orthorhombic tungsten bronze structure, with space group Pba2（ 32 ） and lattice parameters a = 12.6115（2）A, b = 12.4981（2）A, C = 3.9479（3）A. The X-ray powder diffraction lines of the compoutid were well indexed.

关键词： nlobate ziac niobate structure XRD

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Fractal Analysis of Gas Diffusion Layer in PEM Fuel Cells

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Journal of Wuhan University of technology(materials Science) 2006年第1期21卷 22-25页

作者：石英肖金生 State Key Laboratory of Advanced Technology for Materials Synthesis and Processing Wuhan University of Technology Wuhan 430070ChinaSchool of Automation Wuhan University of Technology Wuhan 430070 China State Key Laboratory of Advanced Technology for Materials Synthesis and Processing Wuhan University of Technology Wuhan 430070ChinaSchool of Automotive EngineeringWuhan University of Technology Wuhan 430070China

The aim of this study is to show how fractal analysis can be effectively used to characterize the texture of porous solids. The materials under study were carbon papers, the backing material of the gas diffusion layer （GDL） in Proton Exchange Membrane Fuel Cell （PEMFC）. The fractal dimensions were calculated by analyzing data from mercury porosimetry. The polytotrafluoroethylene （PTFE） treated carbon paper shows a significantly high fractal dimension value than pare sample, and the high fractal dimension signifies that the physical complexity of the pore surface is enhanced. The fractal dimension can be used as a valid parameter to monitor the textural evolution of the samples as the treatment progresses, as this behaves in a similar way to other textural parameters. The use of fractal analysis in conjunction with the results of classical characterization methods leads to a better understanding of textural modificatious in the processing of materials.

关键词： PEMFC gas diffusion layer fractal dimension mewury porosimetry

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Study on the isothermal oxidation behavior in air of Ti_(3)AlC_(2) sintered by hot pressing

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Science China(Technological Sciences) 2006年第5期49卷 513-520页

作者： XU Xuewen1, 2, LI Yangxian1, MEI Bingchu2, ZHU Jiaoqun2, LIU Heyan1 & QU Jingping1 1. School of Material Science and Engineering, Hebei University of technology, Tianjin 300130, China 2. state key laboratory of advanced technology for materials synthesis and processing, Wuhan Univer- sity of technology, Wuhan 430070, China 1. School of Material Science and Engineering Hebei University of Technology Tianjin 300130 China 2. State Key Laboratory of Advanced Technology for Materials Synthesis and Processing Wuhan University of Technology Wuhan 430070 China

The isothermal oxidation behavior at 900–1300°C for 20 h in air of bulk Ti3AlC2 with 2.8 wt% TiC sintered by means of hot pressing was investigated in the work. The isothermal oxidation behavior generally followed a parabolic rate law. The parabolic rate constants increased from 1.39×10[10] kg[2]·m[4]·s[1] at 900°C to 5.56×10[9] kg[2]·m[4]·s[1] at 1300°C. The calculated activation energy was 136.45 kJ/mol. It was demonstrated that Ti3AlC2 had excellent oxidation resistance due to the continuous, dense; adhesive protect scales consisted of a mass of α-Al2O3; a little of TiO2;/or Al2TiO5. In principle, the oxide scale was grown by the inward diffusion of O[2]; the outward diffusion of Ti[4+]; Al[3+]. The rapid outward diffusion of cations usually resulted in the formation of cracks, gaps,; holes.

关键词： Ti3AlC2, oxidation behavior, kinetics.

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Electronic Structure and Thermoelectric Properties of Na and Ni-doped Ca_3Co_2O_6

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Journal of Wuhan University of technology(materials Science) 2006年第3期21卷 94-96页

作者：闵新民 Department of Applied Chemistry Wuhan University of Technology Wuhan 430070 ChinaState Key Laboratory of Advanced Technology for Materials Synthesis and ProcessingWuhan University of Technology Wuhan 430070China

The electronic structures of Ca3Co2O6, Na and Ni doped models were studied by the quantum chemical software of Cambride Serial Total Energy Package （CASTEP） that is based on deusity function theory （DFT） and psendo-potential. The electronic conductivity, seebeck coefficient, thermal conduetivity and figure of merit （Z） were computed. The energy band structure reveals the form of the impurity levels due to the substitutional imapurity in semiconductors. Na-doped model stunts the character of p-type semiconductor, but Xi-doped model is n-type semiconductor. The calculation results show that the electric conduetirity of the doped model is higher than that of the non-doped model, while the Seebeck coefficient and thermal conductivity of the doped model are lower than those of the non-doped one. Because of the great increase of the electric conductivity, Z of Na- doped model is enhanced and thermoelectric properties are improved. On the other hand, as the large decline of Seebeck coefficient, Z of Ni-doped model is less than that of the non-doped model.

关键词： cobalt oxide substitutional impurity quantum chemical calculation electronic structure thermoelectric property

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Electronic Structure and Chemical Bond of Ti_3SiC_2 and Adding Al Element

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Journal of Wuhan University of technology(materials Science) 2006年第2期21卷 21-24页

作者：闵新民 Department of Applied Chemistry Wuhan University of TechnologyWuhan 430070ChinaState Key laboratory of Advanced Technology for Materials Synthesis and ProcessingWuhan University of TechnologyWuhan 430070China

The relation among electronic structure, chemical bond and property of Ti3SiC2 and Al-doped was studied by density function and discrete variation （ DFT- DVM） method. When Al element is added into Ti3 SiC2 , there is a less difference of ionic bond, which does not play a leading role to influent the properties. After adding Al, the covalent bond of Al and the near Ti becomes somewhat weaker, but the covalent bond of Al and the Si in the same layer is obviously stronger than that of Si and Si before adding. Therefore, in preparation of Ti3 SiC2 , adding a proper quantity of Al can promote the formation of Ti3 SiC2 . The density of stnte shows that there is a mixed conductor character in both of Ti3 SiC2 and adding Al element. Ti3 SiC2 is with more tendencies to form a semiconductor. The total density of state near Fermi lever after adding Al is larger than that before adding, so the electric conductivity may increase after adding Al.

关键词： Ti3SiC2 doping of Al electronic structure chemical bond

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High-temperature oxidation behavior of Ti_3AlC_2 in air

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中国有色金属学会会刊：英文版 2006年第B02期16卷 869-873页

作者：徐学文李养贤朱教群梅炳初 School of Materials Science and EngineeringHebei University of Technology Tianjin 300130China State Key Laboratory of Advanced Technology for Materials Synthesis and Processing Wuhan University of Technology Wuhan 430070China

Not only the isothermal oxidation behaviors at 900-1 300℃for 20 h in air of bulk Ti3AlC2 with 2.8% TiC which was sintered by hot pressing with the additive of silicon, but also the cyclic oxidation behavior at 1 100-1 300℃for 30 cycles, were investigated by using TG, XRD, SEM. The isothermal and cyclic oxidation behaviors generally follow a parabolic rate law. The parabolic rate constants of the former increased from 1.39×10-10 kg2/(m4·s) at 900℃to 5.56×10-9 kg2/(m4·s) at 1 300℃. The calculated activation energy is 136.45 kJ/mol. The oxidation products areα-Al2O3 and little TiO2 at 900-1 000℃, however when the temperature is raised up to 1 200℃, TiO2 partially reacts to Al2TiO5, and the reaction is completed at 1 300℃. This demonstrates that Ti3AlC2 has excellent oxidation resistance and good thermal shock because the dense continuous oxide scale consists of massα- Al2O3 and little TiO2 and/or Al2TiO5. Generally, the oxide scale is grown by the inward diffusion of O2- and the outward diffusion of Ti4+ and Al3+.

关键词：三元迭层陶瓷 Ti3AlC2 空气高温氧化行为动力学

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